MHA Story And Quirk Ideas

Quirk: Parry

Izuku's quirk is a summonable Shield made from a (possibly) previously unknown material compound and is virtually unbreakable, as well as immune to destructive quirks. (They just refuse to activate on it for whatever reason) [So Decay, Overhaul etc etc]

(Vibranium from Marvel was my idea[the stuff Captain America's Shield is make of] but you could make it a completely impossible to replicate material as well. Just thought that people trying to study the atomic makeup of Izuku's shield would make things interesting for original plot lines)

Izuku's bones get denser the older Izuku gets. Before he manifested his Shield, his quirk was thought to be Dense Bones. His muscles also healed slightly faster, however it was ONLY his muscles. (So Minor Regen but only for his muscles, to help build up his muscles. After all, the way you get muscles are by breaking your muscles through exercise and them healing overnight. The Regeneration would make the process faster.)

(Basically his body is constantly building itself up to be able to withstand huge hits with his Shield, as if he took a hit from an opponent that was physically stronger than him at full power; if his muscles and bones weren't enhanced the Shield wouldn't break but his bones would. Unless you choose the Vibranium option. However this process stays even if it was Vibranium, as if the Shield couldn't take the hit, it would sacrifice shielding the weilder of the kinetic energy instead of breaking.)

The Shield has a special ability. It allows the user to Parry anything and either send it back at the other person, or break their guard and stun them. (Literally the parry ability from BOTW)

If you need examples to visualize the two, here are some.
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vvvvv  Projectile parry example  vvvvv

vvvvv    Melee parry example     vvvvv

(This includes fists and weaponless combat)
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A cool but practically useless feature about Izuku's Shield is that when he summons it, if he pictures what he wants it to look like in his mind while summoning it, It will look like that. (So if he imagines the color scheme and the minor detailing of the Shield it will change color. The only feature that it could be good for is if Izuku thinks about it being invisible or the front being slightly spikey while summoning it)

Downsides:

Izuku needs to block or parry attacks. This means that if an opponent is faster than him he may not be able to react in time to do so.

Constant reflex and sense training is a must with this quirk. While his quirk reinforced his body, his reflexes and senses aren't enhanced at all. This means he has to constantly train them.

Since gaining muscle is easy for Izuku, training the non-enhanced parts of him is slower to him. This might lead to him getting stressed and/or frustrated with their progress from time to time.

This quirk is purely focused around counterattacking. It has little to no offensive capability besides Shield bashes and charges.

If enhanced by OFA or a Quirk Awakening:

The Shield gains the ability to appear anywhere on his body, instead of on just his arms.

His Muscular Regeneration levels up to Intermediate Regeneration. His skin, organs and bones gain Minor Regeneration properties.

Super Strength.